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Convert Any Flashlight to a Night Vision Ready Red

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As many astronomy gazers might discover, dark adaption is the utmost priority in viewing the night sky. And, unless you're simply enjoying all those "random" little dots of light far over head, viewing star maps is a must--and therefore requires a flashlight for reading them. However, using the right light is imperative for preventing loss of dark adaption.

On a Budget and Too Many Flashlights Doing a quick Internet search turns up a variety of LED and "red" specialty flash lights for astronomy/dark adapted eye use. However, everything comes at a cost, and I'm on a tight budget. Furthermore, I have more than enough variety of flashlights around the house, they just aren't red!

So the problem is, how do I make any number of these flashlights useful for dark adaption use, modify them so everyone in the family has their own, and keeps the costs down? It's simple...

I've discovered photographic "light filter film" which is produced to various light transmittance specifications. What I have found optimal is the Roscolux Orange Red, balanced with an output (when a lightsource it passed through it) of 540 to 660nm. Perfect for a dark red which won't affect eyes when dark adapted.

This light filter film is exceptionally affordable, $6.50 for a 20"x24" the last time I checked. This amount is more than ample for all of the flashlights I intend on using. An Internet search for "Roscolux Orange Red" should get you on the path to many vendors selling this material.

Using the Film

The easiest way to apply this film and convert any household flashlight to a "red" astronomy flashlight is to cut out the shape of the flashlight head, with atleast an extra 1/2" tab on opposing sides . From there, simply use some electrical tape and make sure the film is secure against the front portion of the flashlight lens.

I use black electrical tape to seal up and attach the film to each flashlight.

And that's it. A $6.50 solution to converting all those flashlights and putting them to good use.

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